This invention relates to improvements in log charger systems for veneer lathes. More particularly the invention relates to improvements in such charger systems having automated scanning equipment for sensing the shape of a log and positioning the log for optimum production of veneer.
In the design of veneer production equipment, the primary objectives are to maximize the yield of usable veneer from the irregularly-shaped logs from which the veneer is peeled, and to maximize the production rate of the veneer. In order to attain these objectives great effort has been expended in the development of sophisticated, automated log scanning equipment, primarily of the electro-optical type, for sensing the shape of each log and rapidly determining its longitudinal axis for optimum veneer production. Examples of such scanning systems used or usable for this purpose are contained in the following U.S. Pat. Nos.: 3,736,968; 3,746,065; 3,787,700; 3,852,579; 3,890,509; 3,902,539; 3,992,615; 4,197,888; and 4,221,973. Electro-optical scanners constructed in accordance with the foregoing technology, and particularly those which rotate the log during the scanning process, are extremely accurate and have the capability of determining the location of the log axis for optimum veneer production to within a few thousandths of an inch.
While such a high degree of accuracy in determining the optimum peeling axis should theoretically maximize the yield of veneer from each log, the results obtainable in practice have unfortunately fallen short of this goal because the mechanical log manipulators of veneer lathe chargers are incapable of duplicating the scanner's degree of accuracy. Thus, although the scanning system may identify the location of the optimum peeling axis of a log to within a few thousandths of an inch, the mechanical log manipulators responsible for aligning such axis with the rotational axis of the lathe actually allow a much wider margin for error than that tolerated by the scanning system. Because of this discrepancy in tolerances between the electro-optical and mechanical portions of veneer lathe chargers, substantial mispositioning of the logs and less than optimum yields persist despite the provision of the highly accurate scanning systems.
The progress of log manipulating mechanisms, as opposed to scanning systems, in veneer lathe chargers is exemplified by U.S. Pat. Nos. 3,037,538, 3,664,395, 3,746,065, 3,752,201, 4,197,888 and 4,246,940. In general, all of such chargers attempt to hold the log at either a prepositioning or a scanning station to determine its optimum peeling axis, adjust the position of the log such that the optimum axis is aligned with a reference axis, and transfer the log to the veneer lathe such that the optimum axis is aligned with the rotational axis of the lathe. In these few mechanical steps, however, there are many opportunities for log positioning errors. Relatively large errors can occur, for example, if at any point from the initiation of scanning to the securing of the log in the lathe, the log is supported by engagement with its curved surfaces at points intermediate its ends, rather than by end engagement. Surface engagement allows variation of log position due to surface irregularities or differences in resistance to compressive forces along the surface area, either of which can shift the position of the log transverse to its optimum axis and thereby cause significant error in the final alignment of the optimum axis relative to the veneer lathe. If scanning is not used the optimum axis is determined from insufficient and inaccurate information regarding the log's profile. But even if highly accurate end-engaging and electro-optical scanning techniques are employed, another problem conducive to log-positioning errors remains due to the large degree of adjusting motion required to align the determined optimum peeling axis of the log with the reference axis. Because present modern chargers attempt to perform all necessary log position adjustments pursuant to a single scanning step, the position adjusting mechanism must often travel distances which are too great to permit fine adjustment as a practical matter.
In addition to mechanical inaccuracy, the speed of log manipulation by veneer lathe chargers has been hampered by unnecessary time lags in the various log manipulating steps prior to the initiation of peeling, thereby adversely affecting production rate.